LiNbO 3 thick films grown on sapphire by using a multistep sputtering process

We present the results of investigations of lithium niobate (LiNbO3) films grown on (0001) sapphire substrate by radio-frequency magnetron sputtering. With the aim of producing thick films we have developed a multistep process. To assess the structural quality of our films, we performed x-ray diffraction, transmission electron microscopy, and atomic force microscopy of the films. The results revealed that the epitaxial structure is verified on sapphire whatever the film thickness. Based on our studies we concluded that the proposed multistep process leads to a good controlled epitaxy of thick LiNbO3 samples on sapphire. Using the prism coupling technique we have characterized the optical properties of the deposited layers. The ordinary (no) and extraordinary (ne) refractive indices are, respectively, 2.289±0.001 and 2.206±0.001 at 632.8 nm, and waveguide losses of 1.2 dB/cm have been demonstrated. In addition, we have qualified the film properties between each growth step and between the substrate to layer interface, directly from the measured optical data.